This invention relates to terminations for sheathed optical fibers.
For many applications, the positioning of the core at the end of an optical fiber is very critical on account of its small size. For some applications, this positioning can be determined optically by directing light down the fiber, and observing from where it emerges. For other applications, this is not convenient, and positioning has to be determined mechanically be reference to a surface which is attached to, or forms part of, the fiber. In the case of a sheathed optical fiber, the sheath itself does not normally provide a satisfactory reference surface because the fiber core and cladding are not necessarily coaxial with the sheath. The cladding is a potentially satisfactory reference surface because the core is normally accurately centered within the cladding. (In the case of a graded index fiber having no distinct separate cladding, the fiber itself is similarly a potentially satisfactory reference surface). An unsheathed fiber is, however, very fragile, and hence it is convenient to provide a mechanical reference surface, in the form of a ferrule, into one end of which the sheathed fiber is inserted and secured with the fiber core lying accurately on axis at the other end of the ferrule. This invention is concerned with the problem of obtaining the necessary fiber alignment at the free end of the ferrule.